1. Field of the Invention
The present invention relates to a new and improved flow promoter for fluidized solids and, more particularly, to an apparatus for promoting the flow rate of solid particulates from a fluidized bed into a downcomer extending downwardly of a discharge outlet formed in a bottom wall of the bed.
2. Background of the Prior Art
In fluidized bed heat generating systems, sometimes the solid particulates that are used as a heat exchange medium are difficult to move out of a fluidized solids bed into a downcomer for continuing circulation or passage through the system. This is particularly true where a downcomer joins a bottom wall of a solids bed container at a squared inlet at right angles to a wall. Oftentimes the solid particulate material at lower levels in a fluidized bed tend to gravitate out and remain in a more or less stationary position in comparison to upper layers of material which are constantly being buoyed upwardly by fluidizing gas and tend to move more freely and with horizontal components of velocity. In either event, it is sometimes difficult to insure high flow rates of material from one fluidized solid bed to other components in a fluidized bed heat generating system.
It is known that liquids tend to flow better into a flared or enlarged entrance opening leading into a duct or pipe in comparison to a squared edge inlet configuration. Fluidized solid particles behave somewhat similar to liquids but are different in several aspects. A flared or enlarged inlet for solid particulates may improve the flow rate into a transport duct, however, sometimes this alone is not enough to provide the desired flow rates of material that is needed for moving material from a fluidized solids bed into a downcomer or the like. One of the reasons or limiting factors in retarding solids flow from a fluidized bed into a downcomer is the fact that the solids must move generally in a horizontal direction or at least with a horizontal component of velocity towards the centerline of the downcomer or discharge outlet.
Experimentation has shown that as the fluidized solids flow downwardly into a downcomer inlet, a void or open space at the center of the downcomer entrance is created. This void area or space results in lower flow rates out of the fluidized bed in comparison to a system wherein the void area is completely or partially filled with the fluidized solid particulates preparing to move downwardly toward a downcomer connected to an outlet of the fluidized bed. If the amount of vertical run of a downcomer between a fluidized solids bed and a next-in-line system component is limited and solids flow rate improvement is needed, a flow promoter in accordance with the present invention has proved especially valuable.
The following patents disclose systems or components wherein solid particulates are flowing or circulating between different locations and the patents employ various means for enhancing the fluid flow of the solid particulates: Hoge U.S. Pat. No. 2,781,300; Kruse, Jr. U.S. Pat. No. 2,916,441; Urquhart U.S. Pat. No. 3,332,853; Tamalet U.S. Pat. No. 3,795,487; Lofgren et al. U.S. Pat. No. 4,346,054; Smith et al. U.S. Pat. No. 4,400,150; Andersen U.S. Pat. No. 4,446,799; Foote U.S. Pat. No. 4,448,134, Claus U.S. Pat. No. 4,574,743; Lee et al. U.S. Pat. No. 4,693,682, Teigen U.S. Pat. No. 4,784,533; and Lork U.S. Pat. No. 4,885,137.